1. Field of the Invention
This invention is related to a fluid coupling torque converter, in particular to a stator blade of a torque converter arranged between the impeller and the turbine, which forms two sections of inner ring and outer ring arranged at a predetermined spacing from each other and has space functions as a slot-shaped passage for passing through from the pressure side of the upstream to the suction side of the downstream.
2. Related Prior Art
The fluid coupling torque converter comprising an impeller, which rotates integrally with the torque axle, a turbine rotated by the oil discharged by the impeller, and a stator, which directs the oil flowing back from the turbine to the impeller in the rotation direction of the impeller, has already been disclosed.
In the above mentioned torque converter, the oil discharged from the impeller flows into the turbine, the turbine is rotated by the flowing energy of the oil, then the flowing oil flows back to the impeller from the turbine to convert the rotating direction of the impeller by the stator. The returning oil flow provides a hydrodynamic force on the suction side of the impeller and the rotation of the impeller is increased, and the process of rotating the turbine is repeated by the oil discharged from the impeller with increased rotation, and thereby the turbine generates greater torque than that of the impeller.
Although the conventional stator for the above mentioned torque converter comprises a sheet shaped blade, when the flow of oil enters the stator, the flow direction of the oil and the entrance direction of the flat plate-shaped blade are at an attack angle such that the flow may not enter smoothly, which causes turbulent oil flow and has the problem of decreasing the torque transmission efficiency of the torque converter due to the dynamic energy possessed by the oil being converted into heat energy and being lost.
Therefore, currently all torque converters comprise wing-shaped or hydrofoil shaped blades. In the wing-shaped blade of the stator as such, when the oil flows into the stator blade, the flow may enter smoothly even at a certain difference in angle between the flow direction of the oil and the entrance angle of the blade due to the geometrical characteristics of the leading edge portion.
However, by observing the oil flow around the wing-shaped stator blade, it has been found that when the wing-shaped blade of the stator is at a stall state, the blade may not convey the flow smoothly even if the stator blade is wing-shaped, as depicted in FIG. 4.
Here, the stall state refers to the state where the speed ratio is zero, and the speed ratio refers to the ratio of the rotation speed between the turbine and the impeller. That is to say, the stall state refers to a state where the impeller receives the power from the engine and rotates at the rotation speed of the engine, and the turbine is at a stop due to the driver applying the brakes.
The oil flow around the stator blade, as shown in FIG. 4, may be described in detail as follows: In a state where the speed ratio is in the stall state or low, the turbine is either at a stop or rotating at a low speed and the flow that has left the turbine outlet enters the pressure side of the stator blade from the lower left side of the leading edge of the stator blade with a relatively large angle of attack. Here, the flow separates from the suction side, accompanied by flow recirculation, and as a result the oil is not conveyed sufficiently to the rotation direction of the impeller. Due to this misaligned flow the hydrodynamic force on the suction side is reduced and the rotation of the impeller may not be achieved to the desired amount, and thereby the performance of the torque converter deteriorates, which is the so-called sag phenomenon.
With the sag phenomenon as such, when the speed ratio gradually increases, the rotational speed of the turbine increases and accordingly the angle of attack of the flow entering the stator decreases leading to smooth flow around the stator blade.
Therefore, to prevent the sag phenomenon at the stall state, the forming of a plurality of openings on the stator blade has been disclosed as one example. However, forming a plurality of openings on the stator blade has the following problems.
Namely, in the case of forming a plurality of openings on the stator blade (8), the high energy flow impinging on the pressure side of the stator blade (8) with a large angle of attack will be transmitted to the suction side through the openings, and the effect of minimizing the loss of momentum due to impact at the pressure side may be achieved, and may somewhat increase the efficiency of the fluid machine. However, as depicted in FIG. 7, this plurality of openings formed on the stator blade may not completely prevent flow separation and recirculation, which have direct influence on the performance of the torque converter. That is, in the case of stall state or low speed ratio, when the flow from the turbine outlet enters the stator blade with a large angle of attack, the flow reaching the front part of the pressure side first flows in the downstream direction of the pressure side or flows around the leading edge, which is in the opposite direction, and becomes separated on the suction side of the stator blade, and only a small amount passes through the openings and forms a flow to the suction side. As disclosed in the aerodynamic theory of wings, blowing through openings does not have much effect to prevent flow separation, but rather suction flow is known for effects preventing flow separation. Therefore, as depicted in FIG. 7, in the suction side of the stator blade (8) having a plurality of openings, flow separation and flow recirculation still occur and as the jet stream which passes through the openings mixes with the main flow, even more turbulence is incurred and a complex flow structure is formed which decreases the performance of the fluid machine.